When it comes to building muscle in the weight room, size doesn’t matter. So before you grab the biggest weight in the rack, consider the latest study from McMaster and Waterloo universities, stating muscle size and strength are not related to the size of the weight lifted.

That’s a bold statement considering the long-held belief that the heavier the load, the bigger the muscles. But the Canadian researchers took tradition to task and found that lifting smaller weights for more repetitions was as effective at building muscle as lifting heavier weights for fewer repetitions, as long as the muscle was appropriately fatigued by the end of the last rep of the set.

To be clear, the definition of a heavy load is 70 to 85 per cent of one repetition maximum (the heaviest load that you can lift once). And the recommended number of repetitions of a heavy load, according to the American College of Sports Medicine, is eight to 12 reps for one to three sets.

Taking on the ACSM, not to mention the gym rats who are wary of change, is no small task, but there were inklings a few years ago that the ACSM’s recommendations are out of date. The McMaster researchers published a couple of studies in 2010 and 2012 that foreshadowed their latest results. This most recent study, published this year in the Journal of Applied Physiology, adds to the growing evidence that bigger isn’t better.

To prove their point, the researchers gathered 49 young men with at least two years of weight training experience, divided them into two groups — one high rep and one low rep — and sent them to the gym, where they worked out four days a week for 12 weeks.

The high-rep group performed three sets of 20 to 25 reps with a load that varied between 30 and 50 per cent of one repetition max (1RM), while the low-rep group performed three sets of eight to 12 repetitions with a load between 75 and 90 per cent of 1RM. The workout consisted of five exercises that targeted both upper and lower body muscles, and each of the subjects had their loads adjusted so that they reached muscular fatigue by the last rep of each set.

At the end of the 12-week program, there was little difference between the amount of muscle and strength gained in the two groups, with the exception of the bench press, where 1RM increased to a greater extent in the low-rep group.

Also worth noting is that there was no difference between the high- and low-rep groups in the surge of muscle-building hormones reputed to occur after a weight-training workout. This suggests that strength training does little to promote a hormonal-based increase in muscular size or strength.

Keep in mind that the results of this study are based on training to muscular fatigue, or what the authors call “muscular failure.” This term can be defined as occurring when exercisers are no longer able to perform an additional repetition while maintaining good form. Basic muscle physiology suggests that only when muscles are taken to full exhaustion do they adapt by building themselves back up bigger and stronger. So the lesson learned from these results is that your muscles don’t care what size weights you lift, as long as you lift enough weight often enough to reach muscular fatigue.

Why has it taken so long to make this discovery? The study’s authors suggest that most researchers use similar training volumes (total number of reps) when studying the effects of weight training, so it makes sense that heavier weights would produce greater muscular fatigue. But when the volume of training was based on the end goal of reaching muscular failure, with the low-weight group able to perform the extra reps necessary to fatigue the muscle, the results showed similar gains in muscle strength and size. In the McMaster study, the subjects in the high-rep/low-weight group performed 38 per cent more reps than the low-rep/high-weight group.

How does this affect the average Joe and Jill’s gym workout? It suggests that anyone looking to build muscle size and strength should focus not on the heft of the weight or an associated recommended number of repetitions, but they should ensure that they perform enough repetitions to take the muscle to full fatigue or failure.

So whether you reach exhaustion doing 50 squats while holding a couple of dumbbells or by performing six squats using a bar loaded with as much weight as you can muster, your muscles will realize the same degree of adaptation. That’s good news for anyone who routinely tries to lift too much weight in an effort to gain the best results. Being more conservative in the amount of weight you lift reduces the risk of injury and ensures that you can maintain proper form throughout your workout — something your body will thank you for later.

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